Method of testing pipes



. May 19, 1942. R. GARDNER 2,283,730

METHOD OF TESTING PIPES Filed May 14, 1940 INVENTOR fioerzf 'ardner BY Z gm) ATTOETNEYS Patented May 19, 1942 I warren STATES azsanc METHOD or TESTING PIPES Robert Irving Gardner, Bakersfield, Calif., as-

signor to Richfield Oil Corporation, Los Angeles, Calif., a corporation of Delaware Application May 14, 1940, Serial No. 325,027

4 Claims.

This invention relates to a method of testing pipes to determine fatigue failures and strength factors, such as'ultimate and fatigue bending strength.

In the use of drill pipe for drilling gas and oil wells by the rotary method, the most common limitation of useful life of drill pipe strings is primarily a function of fatigue. Drill failures, such as twist-cits and wash-outs, usually occur subsequent to the development of fatigue cracks. The greatest single factor of lost time on drilling operations is that consumed in fishing as a result of pipe failures.

The most serious failures generally occur at the last engaged thread of a joint. The loads which are imposed on the pipe strings during rotary drilling operations consists of combined bending, axial tension and compression and torsion. While the average stresses are not high, the constantly reversing loads applied to the pipe string cause localized high stresses. Where notches or rapid changes in cross section occur as at the last thread notch, fatigue failures occur due to these localized stresses.

There are several methods for finding incipient failures of rather large smooth sections which are readily accessible. The methods heretofore available are not, however, particularly applicable to failures of the type which occur at the joints of drill pip stems and which, if not detected, will lead to drill failures and consequent fishing operations.

In the present invention I have provided a method of detecting such failures by means of which tests may be conducted in the field. By supporting a section of drill pipe at the joint to be tested and applying a predetermined load to a free end of the pipe, the amount of deflection when a given load is applied may be observed. If the yield point of the joint being tested is known, it is possible to load the section being tested to a point just under the yield point. If the deflection is greater than that which should be obtained for the given load, an indication of fatigue failure is obtained.

In the accompanying drawing I have shown apparatus suitable for use in practicing the process. In this showing:

Fig. 1 is a front elevation of the testing apparatus showing a portion of a drill pipe string arranged therein for testing; and

Fig. 2 is a sectional view of a portion of a drill pipe joint in which a fatigue crack has formed.

Referring'to Fig. 2 of the drawing, the reference muneral i designates an end portion of a drill pipe which is externally threaded as at 2 and is adapted to be engaged by internal threads 3 formed on the end of a tool joint 4. As shown,

. the last engaged thread 5 of the drill pipe sectionis slightly spaced from the end ofthe threaded portion and it is at this point that the 'greatest'stresses occur in the use of the joint.

In use in rotary drilling, the pipe flexesrapidly and yields at this point both in compression and tension every time a load is applied. After alternately yielding in compression and tension the .steel at this point becomes hard and brittle and is ultimately incapable of further yielding. A minute crack a few thousandths of an inch deep will appear at the point indicated at 6. After the appearance of this crack an extremely sharp notch has replaced the rounded thread root and from this time on failure progresses at a faster rate.

The usual methods of testing to determine fatigue failures, such as the use of X-ray, Magnaflux testing and Tubascoping are not suitable for use in testing drill pipe strings, especially in the field. The first two methods are impractical because of the extreme fineness of the fatigue crack and the irregularity of the cross sections. Tubascoping is useful for visually examining the inside surface of the pipe but is not effective for location of failures of this type because, by the time the failure has progressed to the point where it may be observed by Tubascoping, the difficulties in operation have generally been experienced.

According to the present method I determine such failures as that indicated at 6 in Fig. 2 of the drawing by submitting a section of drill pipe containing the joint to be tested to a bending test. One of the principal advantages of this test is that it can be performed in the field where the drill pipe is to be used. In carrying out the invention I employ a machine comprising a base or table I mounted on suitable supports 8. On the table at spaced intervals I provide roller bearing supports 9 and 9' for a drill pipe section ID to be tested. Between the supports I provide a suitable clamping mechanism H having hand operated means I2 for clamping the drill pipe section in place. The joint l3 to be tested is preferably arranged over the roller bearing .9. A short section 20 of pipe is screwed into the tool joint i3. This pipe extends beneath a hydraulic loading apparatus l4 having a ram I5 which has an engaging head IE to contact with the pipe. A support I! is placed on the pipe over the joint l3 and this support carries an arm l8 on which is mounted a deflection gauge I9, the gauge resting on the pipe as shown.

By suitably spacing the clamp ll, l2 and roller 9 and noting the elastic limit of the pipe material, it is possible to stress the pipe by loading the extension 20 to approximately its elastic limit at the section over the roller 9, but the stresses in all other portions will be less than the elastic limit. The load of the ram may be calculated from the known properties of the pipe and dimensions of the pipe and set up by the use of calculations which are common knowledge. With the last engaged thread of the drill pipe over the roll 9 and with an applied load that is just sufficient to stress the pipe at this point to a point just below its elastic limit stress, no permanent deformation will be produced in a sound piece of pipe. If, however, the pipe has a crack similar to 6 a permanent deformation of the pipe at the section of the crack will be formed, because of the weakening effect of the crack. The permanent deformation will be a slight separation of the sides of the crack and a magnified separation of the indicator I9 from the pipe It]. The end of the pipe may then be cut off beyond the point of failure and rethreaded. As the stress applied to the joint being tested will be a compressive stress in the portions below the center line and tensile stress in the portions above the center line, the sequence of operation should be repeated for at least three equidistant positions on the surface of the pipe in order that the crack or failure 6 will be brought into a position above the center line where the force applied will be tensile stress tending to cause further separation of the sides of the crack.

It will be apparent that the method provides a very simple means for testing drill stem joints and tool joints which, with some experience, can

be used by operators in the field to detect fatigue failures before they reach serious proportions and thereby result in failures within the well.

I claim:

1. The method of testing pipe joints to detect failures which comprises supporting two joined sections of pipe at spaced points intermediate the ends of the joined sections, applying a predetermined bending force less than the yield point of the joint to the pipe adjacent one end, and measuring the deflection at the joint.

2. The method of testing pipe joints to detect failures which comprises supporting two joined sections of pipe at spaced points intermediate the ends of the joined sections, with one of the supports arranged beneath the joint to be tested, applying a predetermined bending force less than the yield point of the joint to the pipe adjacent one end, and measuring the deflection at the joint.

3. The method of testing pipe joints to detect failures which comprises supporting two joined sections of pipe at spaced points intermediate the ends of the joined sections, applying a clamping means to the pipe between the supports, applying predetermined bending force less than the yield point of the joint to the pipe adjacent one end, and measuring the deflection at the joint.

4. The method of testing pipe joints to detect failures which comprises supporting two joined sections of pipe at spaced points intermediate the ends of the joined sections with one of the supports arranged beneath the joint to be tested, applying clamping means to the pipe at a point between the supports, applying a predetermined bending force less than the yield point of the joint to the pipe adjacent one end, and measuring the deflection at the joint.

' ROBERT IRVING GARDNER. 

